The rapid growing of wireless communication data volume and rate significantly raise the power consumption in wireless transmitters, in which the power amplifier (PA) is the key component for energy consumption. Several advanced techniques including Envelope Tracking (ET), Doherty Power Amplifier (DPA), Envelop Elimination and Restoration (EER) have been proposed to improve the Power Added Efficiency (PAE) of PA. Among these techniques, DPA is very promising thanks to its simple structure enabling high average efficiency, which is on the basis of active load modulation.
Although the DPA shows numerous advantages for efficiency enhancement, traditional analog DPA still suffers from imperfection which results in a degraded performance in terms of energy efficiency and operational bandwidth. Traditional DPA design is based on single input configuration that contains an analog power splitter (maybe tunable), fixed phase alignment, carrier PA running on class-AB and peak PA running on class-C mode, as well as an output power combiner. To improve DPA efficiency, several methods are studied, including gate bias adaption, asymmetrical DPA, multi-way DPA, tunable phase alignment, and adaptive power splitting ratio.
In order to obtain the optimal PA performance, the designer needs to manually tune the circuit operation parameters and the tuning process is only valid for fixed operating conditions such as input power, frequency, and signal standard. While in the practical scenarios, the optimal control parameters do vary with changing inputs and circuit states. The compensation circuit part is also complicated and challenging to optimize, making DPA design cumbersome. These are very limitations from pure analog based design.
There is a need for a more flexible architecture such as digital DPAs (DDPAs) to adaptively find the optimal control parameters for various circuit states and input signals of various bandwidths, modulation formats, power levels and modulation formats.